An unstable airmass was in place over the central U.S. on the afternoon of the 20th.  A large area of high pressure aloft was located over the west half of the country, placing Iowa in a large scale northwest flow pattern.  A weak cold front dropped southeast through the Dakotas and approached northwest Iowa.  At the same time, a series of MCS's developed over the Rockies, and rode around the upper level ridge of high pressure.  During the day, the dew points across Iowa warmed into the mid 60s to mid 70s with surface temperatures in the mid to upper 80s.  The lifted index by evening was in the -5 C. range with CAPE values in the 2000 to 3000 J/kg range.  The provided a rich environment for an MCS that approached the state during the later part of the afternoon.  The MCS developed over eastern Wyoming and southwest South Dakota earlier in the day.  As it overtopped the upper ridge, it turned southeast into Iowa.  As it did, the storms took on more of a bow echo appearance and the cluster became a small Derecho.  Early on in the event a tornado touched down briefly in Emmet County north of Gruver.  It was in open fields and caused little damage.  The main mode of severe weather was in the form of high winds.  There were  few hail reports, however with the freezing level above 16,500 feet, hail was limited.  The winds caused widespread damage from Emmet County, east to Winnebago County, then south into the central part of the state about as far south as Interstate 80.  South of this area no damage was reported as the storms weakened rapidly.  Two semi-tractortrailer trucks were overturned in Story County by the high wind about 2 miles west of Nevada.  There was one injury from this.  One of the drivers had to be rescued as he hung over the edge of a bridge.  He was taken to hospital, treated, and released.  There were numerous reports of tree and power line damage over the northwest, north central, and central counties of the state.  High winds blew windows out of a home at the ISU Agronomy Farm.  Structural damage was reported in Marshall County at State Center.  The roof of a large building with a roof of less than two years of age received damage.  A high school roof in Story County at Nevada had its roof partially peeled back as well.  In addition to these reports, there were scattered reports of outbuildings and sheds being flattened by the wind.  Visibility during the high winds was occasionally reduced to near zero in blowing dust by the time the storms reached central Iowa.  The gust front from the storms had moved well ahead of the storms themselves, some 10 to 15 miles ahead, with some of the areas receiving severe winds not receiving any rainfall at all.

Thunderstorm Wind in BOONE, IOWA
From 20-JUN-05 18:17:00 to 20-JUN-05 18:17:00 (CST)
Location: OGDEN
Magnitude: 50 EG
Property damage: 5K
Reported by: EMERGENCY MANAGER

Thunderstorm Wind in GREENE, IOWA
From 20-JUN-05 18:20:00 to 20-JUN-05 18:20:00 (CST)
Location: JEFFERSON
Magnitude: 57 EG
Property damage: 5K
Reported by: AMATEUR RADIO

Thunderstorm Wind in DALLAS, IOWA
From 20-JUN-05 18:24:00 to 20-JUN-05 18:24:00 (CST)
Location: PERRY
Magnitude: 50 EG
Property damage: 2K
Reported by: AMATEUR RADIO

Tornado in EMMET, IOWA
From 20-JUN-05 15:55:00 to 20-JUN-05 15:55:00 (CST)
Location: GRUVER
Tornado F-scale: F0
Reported by: LAW ENFORCEMENT

Tornado touched down briefly in open fields north of Gruver.

Thunderstorm Wind in EMMET, IOWA
From 20-JUN-05 15:55:00 to 20-JUN-05 15:55:00 (CST)
Location: ARMSTRONG
Magnitude: 52 EG
Property damage: 2K
Reported by: FIRE DEPT/RESCUE SQUAD

Thunderstorm Wind in WINNEBAGO, IOWA
From 20-JUN-05 16:10:00 to 20-JUN-05 16:10:00 (CST)
Location: THOMPSON
Magnitude: 50 EG
Property damage: 3K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in WINNEBAGO, IOWA
From 20-JUN-05 16:15:00 to 20-JUN-05 16:15:00 (CST)
Location: FOREST CITY
Magnitude: 50 EG
Property damage: 3K
Reported by: LAW ENFORCEMENT

Hail in KOSSUTH, IOWA
From 20-JUN-05 16:17:00 to 20-JUN-05 16:17:00 (CST)
Location: LAKOTA
Magnitude: 0.75 
Crop damage: 5K
Reported by: TRAINED SPOTTER

Hail in KOSSUTH, IOWA
From 20-JUN-05 16:25:00 to 20-JUN-05 16:25:00 (CST)
Location: BANCROFT
Magnitude: 0.88 
Crop damage: 5K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in WINNEBAGO, IOWA
From 20-JUN-05 16:45:00 to 20-JUN-05 16:45:00 (CST)
Location: BUFFALO CENTER
Magnitude: 57 EG
Property damage: 5K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in WEBSTER, IOWA
From 20-JUN-05 18:15:00 to 20-JUN-05 18:15:00 (CST)
Location: GOWRIE
Magnitude: 50 EG
Property damage: 1K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in GREENE, IOWA
From 20-JUN-05 18:00:00 to 20-JUN-05 18:00:00 (CST)
Location: CHURDAN
Magnitude: 57 EG
Property damage: 10K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in WEBSTER, IOWA
From 20-JUN-05 17:36:00 to 20-JUN-05 17:36:00 (CST)
Location: FT DODGE
Magnitude: 50 EG
Property damage: 2K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in WEBSTER, IOWA
From 20-JUN-05 17:37:00 to 20-JUN-05 17:37:00 (CST)
Location: FT DODGE
Magnitude: 52 EG
Property damage: 2K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in WEBSTER, IOWA
From 20-JUN-05 17:38:00 to 20-JUN-05 17:38:00 (CST)
Location: FT DODGE
Magnitude: 50 EG
Property damage: 2K
Reported by: BROADCAST MEDIA

Thunderstorm Wind in WEBSTER, IOWA
From 20-JUN-05 17:40:00 to 20-JUN-05 17:40:00 (CST)
Location: FT DODGE
Magnitude: 50 EG
Property damage: 2K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in WEBSTER, IOWA
From 20-JUN-05 17:45:00 to 20-JUN-05 17:45:00 (CST)
Location: FT DODGE
Magnitude: 57 EG
Property damage: 3K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in HUMBOLDT, IOWA
From 20-JUN-05 17:46:00 to 20-JUN-05 17:46:00 (CST)
Location: HUMBOLDT
Magnitude: 50 EG
Property damage: 10K
Reported by: AMATEUR RADIO

Thunderstorm Wind in GREENE, IOWA
From 20-JUN-05 18:10:00 to 20-JUN-05 18:10:00 (CST)
Location: SCRANTON
Magnitude: 50 EG
Property damage: 1K
Reported by: GENERAL PUBLIC

Thunderstorm Wind in PALO ALTO, IOWA
From 20-JUN-05 16:58:00 to 20-JUN-05 16:58:00 (CST)
Location: MALLARD
Magnitude: 57 EG
Property damage: 5K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in HUMBOLDT, IOWA
From 20-JUN-05 17:20:00 to 20-JUN-05 17:20:00 (CST)
Location: HUMBOLDT
Magnitude: 52 EG
Property damage: 4K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in HUMBOLDT, IOWA
From 20-JUN-05 17:21:00 to 20-JUN-05 17:21:00 (CST)
Location: RUTLAND
Magnitude: 50 EG
Reported by: AMATEUR RADIO

Thunderstorm Wind in WEBSTER, IOWA
From 20-JUN-05 17:30:00 to 20-JUN-05 17:30:00 (CST)
Location: FT DODGE
Magnitude: 57 EG
Property damage: 10K
Reported by: TRAINED SPOTTER

Hail in WEBSTER, IOWA
From 20-JUN-05 18:15:00 to 20-JUN-05 18:15:00 (CST)
Location: GOWRIE
Magnitude: 0.88 
Crop damage: 5K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in POLK, IOWA
From 20-JUN-05 19:02:00 to 20-JUN-05 19:02:00 (CST)
Location: ALTOONA
Magnitude: 52 EG
Property damage: 1K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in POLK, IOWA
From 20-JUN-05 18:42:00 to 20-JUN-05 18:42:00 (CST)
Location: WINDSOR HGTS
Magnitude: 50 EG
Property damage: 1K
Reported by: NWS EMPLOYEE(OFF DUTY)

Thunderstorm Wind in MARSHALL, IOWA
From 20-JUN-05 19:10:00 to 20-JUN-05 19:10:00 (CST)
Location: STATE CENTER
Magnitude: 61 EG
Property damage: 25K
Reported by: EMERGENCY MANAGER

Thunderstorm Wind in POLK, IOWA
From 20-JUN-05 19:10:00 to 20-JUN-05 19:10:00 (CST)
Location: WEST DES MOINES
Magnitude: 50 EG
Property damage: 1K
Reported by: FIRE DEPT/RESCUE SQUAD

Thunderstorm Wind in POLK, IOWA
From 20-JUN-05 19:12:00 to 20-JUN-05 19:12:00 (CST)
Location: BONDURANT
Magnitude: 57 EG
Property damage: 3K
Reported by: AMATEUR RADIO

Thunderstorm Wind in STORY, IOWA
From 20-JUN-05 18:25:00 to 20-JUN-05 18:25:00 (CST)
Location: AMES
Magnitude: 50 MG
Property damage: 2K
Reported by: AWOS,ASOS,MESONET,ETC

Thunderstorm Wind in BOONE, IOWA
From 20-JUN-05 18:30:00 to 20-JUN-05 18:30:00 (CST)
Location: MADRID
Magnitude: 58 MG
Property damage: 5K
Reported by: AMATEUR RADIO

Thunderstorm Wind in STORY, IOWA
From 20-JUN-05 18:30:00 to 20-JUN-05 18:30:00 (CST)
Location: NEVADA
Magnitude: 50 EG
Property damage: 10K
Reported by: EMERGENCY MANAGER

Thunderstorm Wind in STORY, IOWA
From 20-JUN-05 18:31:00 to 20-JUN-05 18:31:00 (CST)
Location: NEVADA
Magnitude: 57 MG
Property damage: 5K
Reported by: AWOS,ASOS,MESONET,ETC

Thunderstorm Wind in BOONE, IOWA
From 20-JUN-05 18:31:00 to 20-JUN-05 18:31:00 (CST)
Location: MADRID
Magnitude: 50 MG
Property damage: 2K
Reported by: AWOS,ASOS,MESONET,ETC

Thunderstorm Wind in BOONE, IOWA
From 20-JUN-05 18:35:00 to 20-JUN-05 18:35:00 (CST)
Location: BERKLEY
Magnitude: 57 EG
Property damage: 5K
Reported by: AMATEUR RADIO

Thunderstorm Wind in STORY, IOWA
From 20-JUN-05 18:35:00 to 20-JUN-05 18:35:00 (CST)
Location: AMES
Magnitude: 50 EG
Property damage: 5K
Reported by: GENERAL PUBLIC

Thunderstorm Wind in STORY, IOWA
From 20-JUN-05 18:35:00 to 20-JUN-05 18:35:00 (CST)
Location: NEVADA
Magnitude: 50 EG
Property damage: 5K
Reported by: EMERGENCY MANAGER

Thunderstorm Wind in STORY, IOWA
From 20-JUN-05 18:45:00 to 20-JUN-05 18:45:00 (CST)
Location: NEVADA
Magnitude: 50 EG
Property damage: 2K
Reported by: AMATEUR RADIO

Thunderstorm Wind in STORY, IOWA
From 20-JUN-05 18:45:00 to 20-JUN-05 18:45:00 (CST)
Location: NEVADA
Magnitude: 57 EG
Property damage: 15K
Reported by: EMERGENCY MANAGER

Thunderstorm Wind in POLK, IOWA
From 20-JUN-05 18:53:00 to 20-JUN-05 18:53:00 (CST)
Location: ANKENY
Magnitude: 52 EG
Property damage: 10K
Reported by: AMATEUR RADIO

Thunderstorm Wind in POLK, IOWA
From 20-JUN-05 18:57:00 to 20-JUN-05 18:57:00 (CST)
Location: ANKENY
Magnitude: 50 EG
Property damage: 3K
Reported by: EMERGENCY MANAGER

Thunderstorm Wind in MARSHALL, IOWA
From 20-JUN-05 19:00:00 to 20-JUN-05 19:00:00 (CST)
Location: STATE CENTER
Magnitude: 52 EG
Property damage: 3K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in POLK, IOWA
From 20-JUN-05 19:00:00 to 20-JUN-05 19:00:00 (CST)
Location: URBANDALE
Magnitude: 50 EG
Property damage: 1K
Reported by: NWS EMPLOYEE(OFF DUTY)

Thunderstorm Wind in HANCOCK, IOWA
From 20-JUN-05 16:35:00 to 20-JUN-05 16:35:00 (CST)
Location: BRITT
Magnitude: 50 EG
Property damage: 2K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in WEBSTER, IOWA
From 20-JUN-05 18:00:00 to 20-JUN-05 18:00:00 (CST)
Location: GOWRIE
Magnitude: 52 EG
Property damage: 3K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in GUTHRIE, IOWA
From 20-JUN-05 18:30:00 to 20-JUN-05 18:30:00 (CST)
Location: BAGLEY
Magnitude: 50 EG
Property damage: 2K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in DALLAS, IOWA
From 20-JUN-05 18:35:00 to 20-JUN-05 18:35:00 (CST)
Location: DALLAS CENTER
Magnitude: 52 EG
Property damage: 5K
Reported by: LAW ENFORCEMENT

Thunderstorm Wind in STORY, IOWA
From 20-JUN-05 18:25:00 to 20-JUN-05 18:25:00 (CST)
Location: STORY CITY
Magnitude: 50 EG
Property damage: 2K
Reported by: BROADCAST MEDIA

Thunderstorm Wind in BOONE, IOWA
From 20-JUN-05 18:25:00 to 20-JUN-05 18:25:00 (CST)
Location: BOONE MUNI ARPT
Magnitude: 52 EG
Property damage: 5K
Reported by: TRAINED SPOTTER

Thunderstorm Wind in STORY, IOWA
From 20-JUN-05 18:27:00 to 20-JUN-05 18:27:00 (CST)
Location: AMES
Magnitude: 50 EG
Property damage: 1K
Reported by: AMATEUR RADIO

Thunderstorm Wind in BOONE, IOWA
From 20-JUN-05 18:28:00 to 20-JUN-05 18:28:00 (CST)
Location: MADRID
Magnitude: 50 EG
Property damage: 5K
Reported by: EMERGENCY MANAGER